1. Field of the Invention
The present invention relates to an interfacial position measuring method and apparatus for measuring a plurality of interfacial positions within a transparent substrate, which is formed by laminating a plurality of layers, by using an optical system. The present invention also relates to a layer thickness measuring method and apparatus for measuring a layer thickness by using measuring such a plurality of interfacial positions, as well as to an optical disc manufacturing method and apparatus for manufacturing optical discs by executing layer thickness measurement.
2. Description of the Related Art
By virtue of the adoption of blue lasers as a recording light source, optical discs such as HD-DVDs or BD (Blu-ray Discs) have been increasing more and more. Together with this trend, there have been being advanced enhancement of the recording density by shortened wavelengths of laser sources used for recording on the optical disc as well as further multilayering of optical disc recording surfaces aimed at larger capacities. Also, as a result of rotation of an optical disc, an inclination or a warp occurs to the optical disc. With a view to ensuring the operation stability against the inclination or warp, the cover layer of the optical disc through which light is transmitted has been going extremely thin. Under such circumstances, a technique for measuring interfaces between individual layers with high accuracy has been desired to fulfill layer thickness control (film thickness control) of optical discs with high accuracy.
As a conventional interfacial position measuring apparatus, there is provided, for example, a confocal optical microscope of Japanese unexamined patent publication No. H08-160306 A (hereinafter, referred to as Document 1). FIG. 37 is a view showing an apparatus configuration using the conventional optical microscope described in Document 1.
Referring to FIG. 37, in the conventional interfacial position measuring apparatus, first, light from a laser source 210 is formed into a point light source by an fθ lens 213, and applied to a sample surface 230 via an image-forming lens 217 and an objective lens 218. Then, in a confocal optical system, reflected light from the sample surface 230 is received by a one-dimensional image sensor 219 placed at a focal position of the image-forming lens 217. For depth measurement of the sample in this measuring apparatus, a galvano mirror 212 placed within the confocal optical system is driven so that a laser spot focused on a focal plane of the objective lens 218 is moved linearly, by which the sample is scanned. In this case, if there is an interface on the scan line of the laser spot, an optical peak of reflected light occurs at a position corresponding to the one-dimensional image sensor 219. Using this optical peak allows the interface to be measured. Under the progress of scanning with the laser beam by means of the galvano mirror 212, the interface of the sample is measured by moving the sample in height in small steps from below to above, layer thickness and configuration of the sample in a cross-sectional direction can be measured.